I. Field of the Invention
The present invention relates to improvements in or relating to a rocker arm made of ceramics for an internal combustion engine.
II. Description of the Prior Art
Various improvements relating to an internal combustion engine, particularly to its valve drive mechanism have recently been proposed in order to attain a high output and an easy maintenance. For example, a rocker arm entirely made of ceramics or a rocker arm having at its sliding portion a ceramic tip which is embedded in an aluminum main body upon casting has been proposed in order to improve the wear resistivity or durability of the rocker arm used at high engine revolution.
A disadvantage of the rocker arm entirely made of ceramics is that it is liable to be broken when subjected to an excessively large impact load at over-revolution of the engine. When the rocker arm is broken, small pieces of the broken rocker arm intrude into the engine to cause serious damage of same.
Another disadvantage is that when the rocker arm is improved in wear resistivity in the above manner, the wear of the cam is increased considerably.
A disadvantage of the rocker arm provided with the ceramic tip is that it requires a particular treatment at the joint between the ceramic tip and the metal main body, thus increasing the cost.
Another disadvantage of the rocker arm provided with the ceramic tip is that its most largely movable portion is heavy, i.e., has a large inertia mass.